Limbering up for what is likely to be the most bruising phase yet in his bid for the Republican nomination Mitt Romney last night fired a fusillade at his foes from both parties who would paint him as a corporate raider because of his former role as CEO of the venture capital firm Bain Capital.

Speaking on board his chartered aircraft travelling from New Hampshire, where he scored a double-digit victory on Tuesday night, to South Carolina, which holds its primary in 10 days, Mr Romney signalled that he is prepared to take the fight over his career at Bain both to President Barack Obama, whom he hopes to face in November, and to his rivals for the party nomination and in particular Newt Gingrich.

"We have understood for a long time that the Obama campaign would come at us for capitalism but I'm a bit surprised that Gingrich would come forward as first witness for the prosecution," Mr Romney tartly declared to a small group of reporters travelling with him.

Mr Romney knows that a blitz of negative advertising accusing him of being a corporate vulture and a flip-flopper awaits him.

His most forceful parry from on board the Miami Air Boeing 737 last night, was aimed at the President and the embarrassment suffered by the White House after a solar energy company in California, Solyndra, went bust after receiving half a billion dollars in federal money. He said this was a crony capitalism scandal and an example of misguided government meddling in the market.

Behaving a little as if he were the nominee already, he said: "Obama was a venture capitalist at Solyndra... and he was a private equity guy at GM and Chrysler. So I'll be talking about his record when I am facing him."

Mr Romney has criticised the federal government bailout of General Motors in particular, arguing that it unnecessarily put a large stake into the hands of the automotive unions.

Mr Romney prevailed easily in New Hampshire, taking 39 per cent of the vote. The former Massachusetts Governor thus moves forward with daunting momentum: he is cash-rich – his campaign announced it had raised $24m in the last quarter of last year exceeding expectations – and now has a 2-0 record of winning both the Iowa caucuses and the New Hampshire primary.

His best luck may be, however, that the conservatives who distrust him continue to divide their support between his rivals, notably Newt Gingrich and Rick Santorum who came fourth and fifth in New Hampshire with 9 per cent each. Rick Perry, the Governor of Texas, is campaigning hard in South Carolina and also has potentially deep pockets to keep going. As a candidate he has mostly proved dismal, however.

The stakes for all the runners are higher than ever in South Carolina. While Mr Gingrich says he will fight every primary contest all the way until June, he hinted yesterday that this may turn out to be his last stand. And not just his. "If Romney can win South Carolina, he's probably going to be the nominee," he said.

John Sununu, the former Governor of New Hampshire and campaign advisor, discouraged talk of inevitably. "You have to take one state at a time," he said as revellers drifted out of Romney's New Hampshire victory party. "This is going to go on for a long time, that's what we've planned for. But meanwhile we'll take on whoever it is that the field pops up this particular week or particular month."

Mr Romney has several challenges. In South Carolina and Florida, which vote on 21 and 31 January, he must win over conservatives who are wary of his past positions on abortion and gay rights. He has yet to craft a strong response to accusations that he stripped assets and jobs from companies bought by Bain Capital when he led it. A factor that may also come into focus in the American South: his Mormon faith.

Puzzling the pundits meanwhile is what now becomes of Ron Paul and Jon Huntsman, who ostensibly did well in New Hampshire placing second and third with 23 per cent and 17 per cent of the vote respectively.

With his anti-war, small government libertarianism, Mr Paul ran away with younger Republican voters in New Hampshire. While no one sees him as the nominee the party will not be able to ignore him. Yesterday he lashed out at the critics of Mr Romney at Bain Capital. "I just wonder whether they're totally ignorant of economics or whether they're willing to demagogue just with the hopes of getting a vote or two," he said. Mr Huntsman, the former Utah Governor, and the only candidate less appealing to conservatives than Romney, vowed for forge ahead even though his cash reserves are dwindling faster than his poll numbers.

New Hampshire poll in numbers

60 Percentage of New Hampshire voters who said the economy is their top priority issue.

12 per cent The proportion of first-time voters that turned out for the GOP primary, a much lower figure than in last week's Iowa caucus.

20 Approximate percentage of voters who waited until the day of the primary to decide on their favoured candidate.

40 The percentage of voters in exit poll who are "dissatisfied" and "angry" with Obama's policies.